1. Field of the Invention
The invention relates to a method of manufacturing a multi-layer coil and a multi-layer coil device and, more particularly, to a method of manufacturing a multi-layer coil by a plating process with varied current densities and a multi-layer coil device utilizing the multi-layer coil.
2. Description of the Prior Art
A choke, which is one kind of multi-layer coil device, is used for stabilizing a circuit current to achieve a noise filtering effect, and a function thereof is similar to that of a capacitor, by which stabilization of the current is adjusted by storing and releasing electrical energy of the circuit. Compared to the capacitor that stores the electrical energy by an electrical field (electric charge), the choke stores the same by a magnetic field.
In the past, the chokes are generally applied in electronic devices such as DC/DC converters and battery chargers, and applied in transmission devices such as modems, asymmetric digital subscriber lines (ADSL) or local area networks (LAN), etc. The chokes have also been widely applied to information technology products such as notebooks, mobile phones, LCD displays, and digital cameras, etc. Therefore, a height and size of the choke will be one of the concerns due to the trend of minimizing the size and weight of the information technology products.
As shown in FIG. 1, the choke 1 disclosed in U.S. Pat. No. 7,209,022 includes a core 10, a wire 12, an exterior resin 14, and a pair of electrodes 16, wherein the wire 12 is wound around the pillar 100 of the core 10. In general, the larger an area of the cross section of the pillar 100 is, the better the characteristics of the choke 1 are. However, since the winding space S has to be reserved for winding the wire 12, the area of the cross section of the pillar 100 is limited accordingly, so that saturation current cannot be raised effectively and direct current resistance cannot be reduced effectively. Furthermore, compared with the conventional winding-type coil structure, the wire has to be wound around the pillar by mechanical operation such that the size and thickness of the choke are limited accordingly (e.g. the size of the wire is reduced, the yield rate is reduced due to incorrect operation, and so on).